Splicing system and jack for stressing concrete

ABSTRACT

A system and hydraulic jack are disclosed for stressing concrete structures with stranded steel cable. In one embodiment, a pocket is formed in a concrete slab with two pairs of stranded cables extending in opposite directions in the slab. Each pair of cables defines a plane that is perpendicular to the plane formed by the other cable pair. One pair of cables is passed in a first direction through apertures in a splice block and secured to it with conical grips. The other pair of cables is passed through the splice block and held releasably by a removable fitting. A hydraulic jack having first and second cylinder and piston rod units is then placed over the overlapped free ends of the cable pairs to force the temporary fitting away from the splice block and thereby tension the cable pairs against each other when the cylinder and piston rod units are expanded. The jack straddles the tensioned cables and is supported solely by the cables once suitable tension is achieved to bear the weight of the jack. A second pair of conical grips is located adjacent the splice block on the pair of cables held by the temporary fitting so that when the pressure is released in the jack, the second pair of grips are seated into the splice block to secure that cable pair and complete the stressing splice. Additional tension may be achieved by contracting the jack and taking a new grip on the free ends of the second pair of cables. Since the jack straddles the tensioned cables it is easily removed or placed into operative engagement with the cable pairs by lifting.

United States Patent Stinton [451 Oct. 31, 1972 SPLICING SYSTEM AND JACKFOR [72] Inventor: Frederick M. Stinton, R.R. No. 2,

Woodbridge, Ontario, Canada [22] Filed: May 6, 1970 [21] Appl. No.:35,168

[52] US. Cl. ..254/29 A, 29/452, 52/223 L [51] int. Cl ..E04g.21/12 [58]Field 01 Search ..254/29 A; 29/452; 52/223 R, 52/223 L [56] ReferencesCited UNITED STATES PATENTS 2,761,649 9/1956 Woolcock ..254/29 A3,285,569 11/1966 Marr et a1. ..254/29 A 3,427,772 2/ 1969 Williams..52/223 R 3,456,918 7/1969 Dabney et a1 ..254/29 A 3,491,431 1/1970Pewitt ..29/452 FOREIGN PATENTS OR APPLICATIONS 78,490 1 1/1954 Denmark..29/452 Primary Examiner-Theron E. Condon Attorney-Mann, Brown,McWilliams 8!. Bradway [5 1 7 AB TRA concrete structures with strandedsteel cable. in one embodiment, a pocket is formed in a concrete slabwith two pairs of stranded cables extending in opposite directions inthe slab. Each pair of cables defines a plane that is perpendicular tothe plane formed by the other cable pair. One pair of cables is ipassedin a first direction through apertures in a splice blocl: and secured toit with conical grips. The other ;pair of cables is passed through thesplice block and held releasably by a removable fitting. A hydraulicjack having first and second cylinder and piston rod units is thenplaced over the overlapped free ends of the cable pairs to force thetemporary fitting away from the splice block and thereby tension thecable pairs against each other when the cylinder and piston rod unitsare expanded. The jack straddles the tensioned cables and is supportedsolely by the cables once suitable tension is achieved to bear theweight of the jack. A second pair of conical grips is located adjacentthe splice block on the pair of cables held by the temporary fitting sothat when the pressure is released in the jack, the second pair of gripsare seated into the spliceblock to secure that cable pair and completethe stressing splice. Additional tension may be achieved by contractingthe jack and taking a new grip on the free ends of the second pair ofcables. Since the jack straddles the tensioned cables it is easilyremoved or placed into operative engagement with the cable pairs bylifting.

llQliPEz 15 DQ1 1 18 Figures A system and hydraulic jack are disclosedforstressing PATENTED our 3 1 ma sum 1 0F 5 PATENTED I973 3,701,509

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SPLICING SYSTEM AND JACK FOR STRESSING CONCRETE BACKGROUND AND SUMMARYThe present invention relates to the stressing of concrete structures;and more particularly it relates to the stressing of concrete slabs byapplying tension to cables embedded in the structure and brought into acentral pocket defined in the structure.

In the stressing (that is, the inducing of a compression stress prior toloading) of concrete structures, steel rods, individual strands orcables composed of a plurality of strands are placed in position priorto the pouring of the concrete. Protective sheaths surround the cablesso that the cables may be elongated, under tension within the concrete.After the concrete is poured and set, but before its intended load isplaced on it, a tension force is induced in the cables which are,anchored at each end to the concrete to induce a compression force inthe concrete.

In one known system for stressing concrete slabs, individual wire rodsare secured at one end in the concrete structure and brought out throughan edge (usually vertical) of the slab or other structure. The ends arebrought through an anchor plate; and a hydraulic jack pulls theindividual rods against the edge of the concrete to tension the rods.The rods are then secured to the anchor plate by bolts or other suitablemeans. This method has the disadvantages of requiring workmen to workover the edge of the slab being tensioned.

Another system for stressing concrete brings a plurality of individualstrands of steel into a central pocket. The strands are divided intoopposing sets which extend in opposite directions in the concrete slab.Each set of strands is secured to an anchor plate after passing throughapertures in the complementary anchor plate. A hydraulic jack supportedby the surface of the slab then forces the two anchor plates apart totension the opposing sets of strand; and when suitable tension isinduced in the strands, a wedge is forced between the plates to holdthem permanently apart. After the hydraulic jacking apparatus iscontracted, the opposing sets of strand remain under tension. The jackis then removed and the pocket filled with concrete. This type of systemis described in U.S. Pat. No. 3,285,569.

An improved system and apparatus for the central stressing of concreteis disclosed in my application Ser. No. 596,576 entitled A METHOD FORCENTRAL PRESTRESSING OF CONCRETE, filed Nov. 23, 1966 now abandoned. Animproved jack apparatus for use in the central stressing of concrete isdisclosed in my U.S. Pat. No. 3,371,909 entitled HYDRAULIC AP PARATUSFOR APPLYING TENSION TO CABLES, issued Mar. 5, 1968.

Prior systems have been been costly in installation and difficult inassembly. For example, prior jacks used for central stressing ofconcrete were designed to rest on the upper surface of the concrete thusobstructing access to the assemblies for anchoring the cables to theirassociated anchor plates. Further, some systems employ tendons whichhaveto be fabricated to the desired length at a shop that is, they were notamenable to cutting on the job.

The present system presents an improvement over prior stressingtechniques in its low cost, reliability and in the facility with whichit is assembled. Further, it is preferably used in combination withstrand steel cable (that is, a cable comprising a plurality ofindividual strands twisted together into a unitary cable) which is moredesirable than rigid steel rods or individual separate strands of cable.

In the present system a pocket is formed in a concrete slab with twopairs of cables extending in opposite directions within the slab. Oneend of each pair of cables is secured to the slab or to the other cablepair; and the free ends of each pair extend into the pocket and overlapeach other. Preferably, one pair of cables is arranged to define avertical plane; and the opposing pair of cables are arranged to projectinto the pocket to define a horizontal plane. The pair of cables whichdefines the horizontal plane (sometimes referred to as the horizontalcables) are passed in one direction through a first pair of conicalapertures in a splice block and secured thereto by means of conicalgripping members. The pair of cables that defines the vertical plane(the vertical cables) are passed in the opposite direction through asecond pair of conical apertures in the splice block, through conicalgripping members (but not at this time tightly secured thereby), andthen secured at their free ends to temporary gripping members orfittings which are adapted to fit overall four cables but are secure toonly the vertical cables. Thus, prior to tensioning there are afirstpair of conical grips securing the horizontal cables to the spliceblock, a second intermediate pair of conical grips adjacent the spliceblock, but not seated in it, and a pair of temporary fittings secured tothe vertical cables.

An expandable hydraulic jack is then lowered into the pocket and adaptedto fit over the arrangement of cables between the splice block and thetemporary fittings. The jack comprises first and second doubleactingcylinder and piston rod units which straddle the cables. The cylindersare connected together by a first yoke frame which engages the spliceblock; and the cylinder jackets are connected together by a yoke framewhich engages the temporary fittings. When the jack is expanded, thesplice block and the temporary fittings are forced apart to tension thecables against each other; and when sufficient tensioning force isinduced in the cables, the jack is supported solely by the cables.

A pair of fingers is arranged on the yoke frame connecting the pistonrods of the jack; and it straddles the vertical cables to hold thesecond pair of conical gripping members near the splice block as thevertical cables are pulled through this second pair of conical grips.

Thus, as the pairs of cables are tensioned against each other, theintermediate pair of grips remains in proximity to their associatedseating surfaces in the splice block by means of these fingers. When thejack has reached its full extension or when sufficient tension force hasbeen induced in the cables, the jack may be retracted slightly so as toseat this intermediate pair of grips in the splice blocks so that thepairs of cables are spliced together through the agency of the spliceblock. If it is desired to further tension the cables, the jack may becompletely retracted and the temporary fittings moved further along thefree ends'of the vertical pair of cables. When the jack is then againexpanded, the intermediate pair of grips will become slightly unseatedto permit the vertical cables to pass further through the splice block;and the jack may be continued to be expanded while maintaining theintermediate pair of conical grips adjacent the splice block. Theprocedure may be repeated as often as is necessary to induce the propertension in the cables; and once the jack is finally retracted, thesplice becomes permanent and very reliable.. The pocket may be filled inwith concrete to cover the splice after removing the jack and thetemporary fittings and cutting the vertical cables, if necessary.

The present invention provides a convenient technique for stressingconcrete which is easily assembled in the field. A single block is usedto splice two pairs of cables together; and the arrangement of the jackwith double-acting cylinder and piston rod units straddling the cablespermits access to the splicing mechanism. By resting the jack solely onthe tension cables, greater accuracy is achieved in effecting thedesired induced tension.

Other features and advantages of the instant invention will be apparentto persons-skilled in the art from the following detailed description ofa preferred embodiment accompanied by the attached drawing whereinidentical reference numerals will refer to like parts in the variousviews.

THE DRAWING FIG. 1 is a schematic showing in plan view of a preferredlayout of strand cable according to the present invention;

FIG. 2 is a perspective view of the components of the inventive systemwith the hydraulic jack out of the pocket;v

FIG. 3 is an exploded perspective view of the arrangement of permanentand temporary cable grips employed in the inventive system;

FIG. 4 is an exploded view of a preferred conical gripping memberemployed in the inventive system;

FIG. 5 is an end elevation view of a preferred splice block and thearrangement of cablesthcrein;

FIGS. 6-10 are diagrammatic illustrations of the successive steps fortensioning cables according to the invention;

FIG. 11 is a perspective view of the inventive jack taken from theunderside;

FIG. 12 is a left side end view in elevation of the hydraulic jackillustrated in FIG. 11;

FIG. 13 is a vertical cross-section view of the piston rod framingmember of the jack of FIG. 11 showing the retaining fingers; and

FIGS. 14-15 illustrate a use of the inventive jack for tensioningsuccessively formed slabs with abutting edges.

' DETAILED DESCRIPTION Referring first to FIG. 1, a chain line definesthe interior border of a pocket formed in a concrete slab the cable pair12); and corresponding cables are preferably permanently securedtogether as at 15. The connection 15 may be performed prior to pouringthe concrete slab or those ends of the cable pairs may also be formedinto a pocket if the width of the U-shape is such as to causesubstantial friction between the cables and concrete defining thechannel in which the cables are laid. It has been found that by placingthe straight portions of the cable pairs at a distance of about 2 feet,one end of each of the cables may be permanently secured so that onlyone splice connection need be made in a pocket for each set of fourcables. When the radius of the U-shape is relatively small, a braceplate 16 may be employed to cushion the pressure of the cables againstthe concrete when tension force is induced in the cables. The cables areenclosed in protective sheaths (not shown) so that they may beelongated, by applied tension, within the concrete. In lieu of thelooped cables as shown in full line in FIG. I, the pair of cables may bedefined by a single cable looped around a plate 16' as shown in dottedlines in FIG. 1, in which case fitting '15 is omitted.

As shown in FIG. 1, the pair of cables 12 are placed directly above andbeneath each other respectively so that their centers define a verticalplane; and these are the so-called vertical pair of cables. On the otherhand, the centers of the cable pair 13 define a horizontal plane. Itwill be appreciated that, although in the preferred embodiment, theplane defined by the centers of the cable pair 12 is perpendicular tothe plane defined by the centers of the cables of pair 13, otherarrangements may be employed as to minimize any coupling moment inducedon the final splicing block permanently fastening the two pairstogether.

Turning now to FIG. 2, the pocket 10 has a rectilinear shape; and itincludes first and second opposing vertical side walls 10a and 10b outof which the free ends of the cable pairs 12 and 13 project respectivelyin overlapping relation. The pocket 10 may be formed by any of a numberof known techniques.

The individual cables comprising the cable pair 12 are designated A andA; and the individual cables comprising the pair 13 are designated B andB respectively. Each of the cables A, A, B and B may comprise sevenindividual strands twisted into a unitary cable, each strand being awire of hardened structural steel having a diameter of threethirty-seconds inch.

In FIG. 2, the cable pairs 12 and 13 are shown in a state wherein theyhave been tensioned to a predetermined level and permanently securedtogether by means of a splice block 20. This connection is referred toas a stressing splice. After the cable pairs have thus been permanentlyspliced together, the pocket 10 may be filled with concrete and the freeends of the cables as well as the splice block 20 permanently embeddedin the concrete. In one embodiment, the splice block 20 is a disc ofhardened, high-strength stainless steel having a diameter of 3% inch anda thickness of 1% inch. Splice block 20 is also shown in the lowerright-hand corner of FIG. 2; and it is seen to include four separateapertures. designated respectively 22, 23, 24, and 25. Each of theapertures 22-25 is frusto-conical in shape to provide a bearing surface;and the axis of each aperture is parallel to the axis of the cylindricalside wall 21 of the splice block 20. The taper of two opposing apertures(for example, apertures 22-and 24) is opposite in direction to the taperof the other pair of apertures (23 and 25 in this example). The pairs ofcables 12 and 13 are received in opposite ones of the apertures 22-25and pass through their respective aperture in the direction ofincreasing diameter of the seating aperture for reasons presently to beexplained. The axes of the apertures 22-25, in transverse section,define a square centered on the axis of the cylindrical side wall 21.

A frusto-conical (or simply conical) gripping member, such as the onegenerally designated 26 in FIG. 2 and seen in exploded view in FIG. 4,receives each of the stranded cables and seats into one of the apertures22-25 of the block 20 to permanently secure its associated cable to thesplice block. Preferably, each gripping member includes three separatesections or wedges; and these are designated 27, 28 and 29 in FIG. 4.When placed together in abutting relation, the wedge sections 27-29define a central cylindrical aperture of uniform diameter for receivingone of the stranded cables while at the same time providing afrusto-conical bearing surface for seating into one of thefrusto-conical apertures in the splice block so as to fully engage theseating surface and thereby spread the force over an extended area. Insome cases the central aperture may be frusto-conical rather thancylindrical. A split ring 30 is received in a peripheral groovegenerally designated 31 formed in the exterior conical seating surfaceof each of the wedge sections 27-29 at a location adjacent the widestexterior diameter of the grip. The ring 30 spring-biases all of thewedge sections into a closed or retracted state yet permits theexpansion of the individual wedge sections to receive the strandedcable.

FIG. 5 is an end view of the splice block 20 showing the seatingapertures 22 and 24 for receiving the vertical cables A and A' having anexpanding diameter into the plane of the page and the other apertures 23and 25 having a reduced diameter into the plane of the page of thedrawing. The axis of each aperture is equidistant from and parallel tothe axis of the cylindrical side wall 21.

The interior cylindrical surfaces of the wedge sections may be groovedcircumferentially to provide teeth for better gripping of the strandedcable.

Referring now to FIGS. 2, 11 and 12, a hydraulic jack for applyingtension to the cable pairs is generally designated by reference numeral33. The jack 33 includes first and second hydraulic cylinder and pistonrod units generally designated 34 and 35. The cylinder and piston rodunit 34 includes a piston rod 36 and a cylinder jacket 37 which definesa cavity, as is well known in the art, for receiving fluid underpressure to bear against a piston head attached to the rod 36 to movethe rod 36 to an expanded or extended state. Similarly, the unit 35includes a piston rod 38 and a cylinder jacket 39; and an input conduit40 feeds the cavities of each of the units 33 and 34 to expand the rods36 and 38 in unison. The input conduit 40 is connected to a header 41;and conduits 42 and 43 feed respectively the cavities of the units 33and 34. A return conduit 45 is similarly connected to the rod side ofthe piston as a return conduit, as is also well known.

The butt ends of the cylinder jackets 37 and 39 are rigidly connectedtogether by a transverse frame member 46 which is integrally formed withside cylindrical rings 47 and 48 connected respectively to the butt endsof the cylinder jackets 37 and 39. A second frame 50 similarlyinterconnects the neck ends of the cylinder jackets 37 and 38 so that asolid, rigid unitary frame is formed by means of the cylinder jackets 37and 39 and the frame members 46 and 50. A third frame member 51 (seenbest in FIG. 11) in secured to the distal ends of the rods 36 and 38 bymeans of bolts 52 and 53 so that the rods are also rigidly connectedtogether and move in unison when expanded and retracted. Still referringto FIG.-11, each of the frame members 46, 50 and 51 is in the form of ayoke, defining a central aperture communicating with the exterior of thejack (designated respectively 46a, 50a, and 51a) so that the entire jackmay be set upon the stranded cables and removed therefrom simply bylifting. The aperture 46a further includes a vertical groove 46b forreceiving the uppermost cable A, and first and second horizontalshoulders 46c and 46d for resting respectively on the horizontal cablesB and B. The aperture 500 in the framing member 50 may be identical tothe aperture 46a as just described.

Referring now to FIG. 12, the aperture 51a in the yoke frame 51 for thepiston rods is provided with a vertically-extending aperture forreceiving the uppermost cable A, and with inclined surfaces 51b and 51c.A fork generally designated by reference numeral 56 in FIG. 13 islocated inboard of the yoke-frame 51 and includes first and secondvertically depending fingers 57 and 58 spaced apart at a distancesufficient to receive both of the vertical pair of cables A and A, asseen in FIG. 12. When the jack is lowered onto the cables fortensioning, the horizontal pair of cables B and B are located within theaperture 51a but outside of the fingers 57 and 58 thus, the inclinedsurfaces 51b and 510 engage the cables B and B respectively for supportwhen the cables are stressed.

Referring now to FIGS. 11 and 12, a brace bar 59 is secured to theoutboard face of the yoke frame 51 for rigidity; and extending from itslower surface is a semicylindrical hub 60 for receiving the disc-shapedsplice 20. The hub 60 is also provided with an inwardly-projectingcurved lip 61 which is spaced from the surface of the splice block 20.Thus, when the jack 33 is lowered onto the cables, the splice 20 isreceived in a vertical direction within a cavity defined by the hub 60,lip 61, and frame 51. The hub 60 is located relative to the face of theframe 51 such that when the splice 20 is thus received, the cables A, A,B and B are located as illustrated by dashed line in FIG. 12. When thejack is thus placed on the splice block, and the splice is secured tothe cables, the frame member is constrained against longitudinalmovement of the cables B and B.

As seen in FIGS. 2 and 13, an aperture 65 is formed vertically in theyoke frame 51 between the fork 56 and the brace bar 59 for receiving atool 66 (FIG. 2) having two prongs 67 and 68 spaced apart to define anaper ture 69 for permitting the tool to be placed over the cables A andA when the tool 66 is lowered into the aperture 65. The prongs 67 and 68are tapered to form a decreasing width or wedge for reasons presently tobe made clear.

Still referring to FIG. 2, two temporary seating blocks are designated70 and 71 in the right side of the drawing; and since they may beidentical, only the seating block 70 will be described in greaterdetail. The seating block 70'includes a base 72 defining first andsecond semi-cylindrical grooves 73 and 74 for fitting over (or under asin the case of the temporary seating block 71) the pair of horizontalcables B and B. Integral with the base 72 is a cylindrical extension 75defining a frusto-conical seating surface 76 for receiving a temporarygrip which may be identical to the previously-describedv conical grip26. The aperture defined by the cylindrical seating surface 76 communicates with a cylindrical aperture in the base 72 for receiving one ofthe pair of cables A, A. The other temporary seating block 71 isintended to be similarly fit over the other of the cable pair A, A, sothat the semi-cylindrical grooves on each block cooperate to receive thehorizontal cable pair B, B.

Referring now to FIG. 3, there is shown in exploded view, an assemblageof the splice block 20, the first and second pairs of permanent gripmembers, and the temporary seating blocks 70 and 71. As will be recalledfrom the description accompanying FIG. 2, the cable pair A, A define avertical plane; and they are passed through the splice block 20 andthrough their associated conical seating apertures designatedrespectively by reference numerals 22 and 24. It will be noted that thecables are all passed through the seating apertures in the splice blockin the direction of expanding diameter. Next, first and second conicalgripping members 82 and 83 of the same type as member 26 are placed overthe stranded cables A and A respectively and adjacentthe seatingapertures 22 and 24 respectively. The grips 82 and 83 are the ones thatwill ultimately be permanently secured to the splice block; but untilthe desired tension is induced in the cables, these grips are not seatedunless it is required to take a new hold with the temporary grips, aspresently to be described.

The horizontal cables B and B are then passed respectively through theirassociated conical seating apertures 23 and 25 (again, the cables arepassed in the direction of expanding aperture diameter). A second pairof conical grips 87 and 88 (of the same type as grip 26) are then placedover the free ends of the cables B and B respectively and into theconical seating apertures 23 and 25 of the splice block 20. The grips 82and 83, together with the previously mentioned grips 87 and 88, are thepermanent grips which will remain in contact with the splice block 20after the splice is completed.

Next, the free end of cable A is passed through the cylindrical aperturein the block 71 and the conical aperture in its associated seatingmember 71a. The cable A passes through the aperture of the seatingmember 71a in the direction of expanding diameter so that a temporarygripping member 90 may then be placed over the cables A and fitted intothe seating member 71a. Similarly, the block 70 is passed over the cableA, and a temporary conical grip 91 is fitted into the aperture 76 of theseating'block 70. Grips 90 and 91 are of the same type as grip 26. Thesemi-cylindrical grooves 73 and 74 cooperate with similar grooves on thetemporary block 71 to receive the cables B and B respectively. Thus,prior to stressing there are a first pair of permanent grips (87 and 88)securing the ends of the horizontal cables B and B to the splicing block20, a second or intermediate pair of permanent grips (82 and 82)received on the vertical cables A and A but not secured thereto at thistime, and a pair of temporary fittings (90 and 91) secured to thevertical cables but removable. After all of the elements shown in FIG. 3are placed on the two cable pairs as just described, the jackingapparatus 33 is lowered into the pocket 10 with the semicylindricalcavity defined by the hub 60 and lip 61 (FIG. 11) fitting over thesplice block 20 and the temporary blocks and 71 engaging the verticalsurface of the yoke frame 50 which faces the yoke frame 46 of thecylinder jackets.

The sequence of steps for inducing a predetermined stress in theopposing pairs of cable is illustrated in FIGS. 6-10; however, forclarity, only one of each opposing pair of cables is illustrated; and itwill be understood that what is disclosed in connection with upper cableA is also true for cable A, and whatever is disclosed in connection withcable B is true for cable B, the section shown being taken through thesight line 6-6 of FIG. 5 so that the cable B is rotated to a lowerposition to view the sequence in one plane.

In FIG. 6, the splice block 20 is seen to receive cables A and B inoverlapping relation within the pocket 10. The cables extend in oppositedirections within the slab and are secured to the slab in some suitablemanner (as by the U-shape in FIG. 1 or by end anchorages for fourseparate cables which define the cables A A and B B. The temporaryseating member 70 and its associated temporary fitting 91 are shown inchain line.

Turning now to FIG. 7, the jack 33 is lowered into the position withtheyoke frame 51 (which interconnects the piston rods 36 and 38) fittingover the splice block 20.

It will be observed that all of the four cables A, A, B and B extendthrough the yoke frame members 46, 50 and 51 of the jacking apparatus;and the jack may easily be removed by simply lifting it off the cables.After thejack 33 is lowered to the position shown in FIG. 7, pressurizedfluid is forced into the input conduit 40 on the jack to expand it byextending the piston rods 36 and 38 to force the temporary seating block70 to the right in FIG. 7 and the splice block 20 to the left. Thisinitial motion seats the permanent conical grip 87 into its associatedseating aperture in the splice block 20 to secure the cable B tightly tothe splice 20 and to stress the cable B. Similarly, the temporaryseating block 70, upon being forced to the right, engages the conicalbearing surface of the temporary fitting 91 which, in turn, bites thecable A and forces it to the right to induce a stress in it. At thistime the permanent conical grip 82 is unseated because cable A is beingforced in a direction toward the right and pulls the grip 82 away fromits associated conical seating surface within the splice block 20..However, the fingers 57 and 58 of the fork 56 which is secured to theframe 51 of the jack, limits the rightward motion of the intermediategrip 82 so that it remains in proximity to its associated conicalbearing surface but is permitted to slide along the extending cable A.This motion is illustrated in FIG. 8 wherein the pressurized fluidforces an expansion between the piston rod and the cylinder jacketsthereby inducing equal and opposite stress in the cables A and B.

After a predetermined stress has been induced in the cables A and B (asmay be determined by monitoring the pressure of the fluid in thecylinder), or the jack has reached its full extension, or the jack hasexpanded to a state in which it begins to interfere with the end wallsof the pocket, the tool 66 (FIG. 9) is placed into the aperture 65formed in the frame member 51; and the inclined surface 66a of the tool66 engages the permanent (intermediate) grip 82 and forces it away fromthe teeth 57 and 58 of the fork 56 and into seating engagement with itsassociated conical bearing surface in the splice block 20. Next, thepressure in the cylinders of the jack 33 is reduced so that the jackcontracts; and as it does so, the seating member 82 becomes permanentlyseated in the splice block 20 to securely grip the cable A. The jack maythen be removed (if proper stressing force has been induced in it) or itmay be forced to a fully contracted state to take a new bite and inducefurther stress in the cables. If the jack is fully contracted, the lip61 which engages the outer vertical surface of the splice block 20 willhold the piston rods so that the cylinders of the jack 33 will move tothe left in.FIG. 9. The temporary gripping blocks may then be moved intocontact with the frame member 50 of the jack 33; and the steps of FIGS.7-9 repeated. That is to say, when the temporary fitting 91 is againplaced into engagement with its associated conical bearing surface onthe temporary seating block 70 and the jack expanded, the intermediategrip 82 holding the cable A will become unseated (and held in proximityto the splice block by means of the teeth 57 and 58) so that additionalstress may be induced in the cables if desired. A number of such passesmay be taken. If the temporary fitting 71 becomes secured tightly to thecable A, a tap with a hammer will loosen it. Finally, after the desiredstress has been induced in the cables A and B, the jack may be removed;and the permanent splice is formed as illustrated in FIG. 10. (Again,only for one each of the two opposing sets of cables). By the time thefinal stress is induced, the splice block 20 usually is well toward theleft of the pocket, as seen in FIG. 2.

Turning now to FIGS. 14 and 15, there is shown a modification of theinventive system wherein a number of slabs of concrete may be laidside-by-sidc in succession with adjacent edges abutting so as to form acontinuation surface for use, for example, as an air strip. In FIGS. 14and 15 elements similar to those in FIGS. 1-13 are employed but the jackis not supported on the cables solely. In FIG. 14, the splice block isdesignated 120; and is similar to the previously described splice block20, having two pairs of conical bearing surfaces, each pair tapering indifferent directions axially of the cylindrical side wall of the spliceblock. Again, the one pair of cables is designated A and A, and theopposing pair of cables is designated B and B.

In FIG. 15, a concrete slab is designated by reference numeral 121. Theslab may be of any predetermined length or width; and there may be asmany cable pairs as are required extending through it. The cables B andB are set in position before the concrete 121 is poured and extendedthrough first and second end bearing plates 122 and 122' which arelocated in opposite vertical edges of the slab 121. The cables B and B'are brought out through suitable apertures in the plates 122 and 122. Aleft-side splice or anchor block similar to block 20 may be used tosecure the horizontal cables B and B to the plate 122' by means ofconical grips 123 and 124 which are similar to grips 26. The spliceblock 120 is placed over the cables B and B with conical grips 125 and126 then placed over the cables. A jack 133 is placed over the cablesafter a temporary block 127 is attached to the free end of cables B andB by means of temporary fittings 130 and 131. Jack 133 is similar tojack 33. It may have a rod connecting yoke frame similar to frame 51 forreacting against block 120 and a cylinder connecting frame similar toframe 50 for reacting against temporary fitting 127.

The jack 133 stresses the cables B and B by pushing against the spliceblock 120 which bears against the plate 122, and pushing againsttemporary fitting 127. When the jack is expanded, the permanent grippingmembers 125 and 126 will be unseated so that the temporary fittings 130and 131 pull the cables. After suitable tension has been induced in thecables or it is desired to take a second pull, the hydraulic jack 133may be retracted so that the permanent gripping members 125 and 126become seated in the block 120 and holds the cable under tension againstthe plate 122. Vertical cables A and A (for the subsequently-laidconcrete slab) then may be secured to the splice block 120 by means ofpermanent conical grip extending in an opposite direction to the grips125 and 126. After the cables B and B have been tensioned, the jack isremoved, the cables A and A are anchored in block 120, and a second slabis laid to the right of the slab 121 and contiguous with it. The cablesA and A extend through the subsequently-laid slab and may be tensionedas described above with the jack and other components remainingidentical.

Having thus disclosed in detail a preferred embodiment of the presentinvention, it will be apparent to persons skilled in the art thatcertain modifications may be made to the inventive system withoutdeparting from the principles thereof and that substitutions may be madefor the structure shown while continuing to practice the invention; andit is, therefore, intended that all such modifications and substitutionsbe covered as they are embraced within the spirit and scope of theappended claims.

I claim:

1. A system for tensioning concrete structures comprising first andsecond sets of cables extending respectively in opposite directionswithin said structure and each cable having one end secured relative tosaid structure and a free end extending into a pocket in said structure,the free ends of each set overlapping in said pocket; a splice blockdefining a first set of apertures, each for receiving one of said firstset of cables and a second set of apertures each having an expandingdiameter and defining a tapered seating surface for receiving one ofsaid second set of cables in its direction of expanding diameter;gripping means securing respectively the'free ends of said first set ofcables to said splice block; a set of tapered gripping means received onsaid second set of cables adjacent said splice block and adapted to beseated in an associated one of said tapered apertures therein; temporaryfitting means for releasably holding the free ends of said second set ofcables after passing through said splice block; and expandable hydraulicmeans for engaging said splice block and said temporary fitting meansfor urging the same apart to tension said sets of cables against eachother whereby when said hydraulic means is contracted to release thetension on said temporary fitting means said tapered gripping means willbe seated in said tapered apertures of splice block to secure said setsof cable together, and said hydraulic means and said temporary fittingmeans may be removed.

2. The system of claim 1 wherein said first and second sets of cableseach comprise a pair of stranded steel cables and wherein the taperedseating surfaces of said second set of apertures of said splice blockand said tapered gripping members are frusto-conical in shape.

3. The system of claim 1 wherein said first-named gripping meanscomprises a plurality of frusto-conical grip members, one for each ofsaid first set of cables, and wherein said first set of apertures ofsaid splice block comprises a plurality of frusto-conical seatingsurfaces each receiving one of said first set of cables in the directionof expanding diameter and adapted to receive one of saidfrusto-conicalgrip members for permanently securing said first set of cables to saidsplice block.

4. The system of claim 1 wherein said hydraulic means comprises firstand second cylinder and piston rod units adapted to straddle said firstand second sets of cables and to extend in the direction of elongationof said cables, first yoke frame means interconnecting the rods of saidunits and defining a throughway for fitting over and engaging at leastone of said sets of cables, said first yoke frame means adapted toengage said splice block, second yoke frame means interconnecting saidcylinders of said units and defining an aperture for receiving said setsof wires and engaging at least some of said second set, and bearingsurface means for engaging said temporary fitting means, whereby whensaid units are expanded, said first yoke means will force said spliceblock relative to said temporary fitting.

means to tension all of said cables and at least some of said cableswill engage their associated yoke means to lift said hydraulic meanswhen said cables are under tension.

5 Apparatus for applying tension to first and second sets of spacedcables extending in opposite directions relative to each other with freeends overlapping, the free ends of one set of cables secured to a spliceblock, comprising: first and second cylinder and piston rod unitsadapted to straddle said sets of cables, first frame means fastened tothe piston rods of said units to secure the same together, second framemeans fastened to the cylinders of said units to secure the sametogether whereby said rods move in unison relative to said cylinderswhen said units are expanded, seating means connected to one of saidframe means, said seating means having a surface formed and adapted forreceiving said splice block in seating engagement, the other frame bleswhereby said jack rests on and is supported by said cables whentensioned and it may be removed after said cables have been permanentlyfastened together by contracting and lifting the same transverse of thdirection of elongation of said cables. 4

6. The apparatus of claim 5 wherein said one of said frame meansincludes means for engaging said splice block to limit motion of saidone frame means relative to said splicing block along the direction ofelongation of said cable.

7. The apparatus of claim 6 wherein said one of said frame meansengaging said splice block further includes a vertical aperturecommunicating the upper side of said jack with said splice block forreceiving an inclined tool to tap permanent gripping means intocorresponding seating apertures of said splice block.

8. The apparatus of claim 5 wherein said sets of cables comprise a firstpair of cables having centers defining a vertical plane and a secondpair of cables having centers defining a horizontal plane, and whereineach of said throughways of said yoke frame means comprises a gen-erallyvertical groove for receiving the uppermost of said pair of cablesdefining said vertical plane.

9. Apparatus for applying tension to first and second sets of cablesextending in opposite. directions in a concrete structure and secured attheir respective remote ends to said structure and including free endsextending into a pocket in said structure in overlapping relation, thecables of each set being spaced from one another and the cables of eachset defining a plane with the planes so defined intersecting oneanother, comprising:

first and second cylinder and piston rod units extending in a directionof elongation of said cables when placed in operative relation relativeto said cables and lying on either side of said cables when in saidoperative position; first yoke frame means interconnecting the rods ofsaid units and adapted to fit over the tops of said cables and includingan element formed and adapted to receive a splice block secured to oneof said sets of cables; said element including a flange extendingtransversely to the axes of said cylinders, said flange being spacedfrom said first frame means to provide an abutment for the side of saidsplice block,and second yoke frame means interconnecting the cylindersof said units and adapted to receive all of said cables in a directionperpendicular to the direction of elongation of said cables, said secondframe means providing a bearing surface for engaging a temporary fittingreleasably secured to the other of said sets of cables and remotelylocated from said element.

10. A method of tensioning a concrete structure comprising forming saidslab with an open pocket and first and second sets of cables extendinginto said pocket out of opposing surfaces of said pocket respectively,passing said first set of cables in a first direction through a firstset of apertures in a splice block, passing said second set of cables ina direction opposite to said first direction through a second set oftapered apertures in said splice block in the direction of expandingdiameter of said apertures, securing said first set of cables to saidsplice block, passing a tapered grip on each n,

of said second set of cables adapted to be received in an associated oneof said tapered apertures in said spice block, then forcing said secondset of cables against said splice block by hydraulic means to pull saidsecond pair of cables through said splice block thereby to tension allof said cables, then urging said tapered grips into contact with theseating surface of said second set of apertures, and then releasing theforce exerted by said hydraulic means on said cables to thereby seatsaid tapered grips in their associated apertures and to connect all ofsaid cables directly to said splice block.

11. A fluid pressure operated jack assembly for applying tension tocables embedded in concrete including a pair of fluid cylinders, a firstyoke spanning said cylinders and fixed thereto, a second yoke fixed tothe piston rods of said cylinders, said yokes being formed and adaptedto hold said cylinders in spaced, generally parallel relation, saidfirst and second yokes having recesses formed therein to permit passageof cables through said yokes, the recess in each yoke providing spacedabutment surfaces extending generally parallel to the axes of saidcylinders, and a cable receiving groove between said abutment surfaces,said abutment surfaces being spaced from said groove by additionalsurfaces extending between said abutment surfaces and said groove.

12. The structure of claim 11 wherein one of said yoke includes spacedfingers in the recess therein, the space between said fingerscommunicating with said groove, said fingers being spaced from saidabutment surfaces to allow reception of cables between said fingers andsaid abutment surfaces.

1. A system for tensioning concrete structures comprising first andsecond sets of cables extending respectively in opposite directionswithin said structure and each cable having one end secured relative tosaid structure and a free end extending into a pocket in said structure,the free ends of each set overlapping in said pocket; a splice blockdefining a first set of apertures, each for receiving one of said firstset of cables and a second set of apertures each having an expandingdiameter and defining a tapered seating surface For receiving one ofsaid second set of cables in its direction of expanding diameter;gripping means securing respectively the free ends of said first set ofcables to said splice block; a set of tapered gripping means received onsaid second set of cables adjacent said splice block and adapted to beseated in an associated one of said tapered apertures therein; temporaryfitting means for releasably holding the free ends of said second set ofcables after passing through said splice block; and expandable hydraulicmeans for engaging said splice block and said temporary fitting meansfor urging the same apart to tension said sets of cables against eachother whereby when said hydraulic means is contracted to release thetension on said temporary fitting means said tapered gripping means willbe seated in said tapered apertures of splice block to secure said setsof cable together, and said hydraulic means and said temporary fittingmeans may be removed.
 2. The system of claim 1 wherein said first andsecond sets of cables each comprise a pair of stranded steel cables andwherein the tapered seating surfaces of said second set of apertures ofsaid splice block and said tapered gripping members are frusto-conicalin shape.
 3. The system of claim 1 wherein said first-named grippingmeans comprises a plurality of frusto-conical grip members, one for eachof said first set of cables, and wherein said first set of apertures ofsaid splice block comprises a plurality of frusto-conical seatingsurfaces each receiving one of said first set of cables in the directionof expanding diameter and adapted to receive one of said frusto-conicalgrip members for permanently securing said first set of cables to saidsplice block.
 4. The system of claim 1 wherein said hydraulic meanscomprises first and second cylinder and piston rod units adapted tostraddle said first and second sets of cables and to extend in thedirection of elongation of said cables, first yoke frame meansinterconnecting the rods of said units and defining a throughway forfitting over and engaging at least one of said sets of cables, saidfirst yoke frame means adapted to engage said splice block, second yokeframe means interconnecting said cylinders of said units and defining anaperture for receiving said sets of wires and engaging at least some ofsaid second set, and bearing surface means for engaging said temporaryfitting means, whereby when said units are expanded, said first yokemeans will force said splice block relative to said temporary fittingmeans to tension all of said cables and at least some of said cableswill engage their associated yoke means to lift said hydraulic meanswhen said cables are under tension.
 5. Apparatus for applying tension tofirst and second sets of spaced cables extending in opposite directionsrelative to each other with free ends overlapping, the free ends of oneset of cables secured to a splice block, comprising: first and secondcylinder and piston rod units adapted to straddle said sets of cables,first frame means fastened to the piston rods of said units to securethe same together, second frame means fastened to the cylinders of saidunits to secure the same together whereby said rods move in unisonrelative to said cylinders when said units are expanded, seating meansconnected to one of said frame means, said seating means having asurface formed and adapted for receiving said splice block in seatingengagement, the other frame means providing a surface for engaginggripping means temporarily secured to said second set of cables, saidfirst and second frame means being yokes defining throughways for saidcables between said units, said throughways communicating with theexterior of the jack, said throughways defining spaced surfaces adaptedto engage and rest upon at least two of said cables whereby said jackrests on and is supported by said cables when tensioned and it may beremoved after said cables have been permanently fastened together bycontracting and liFting the same transverse of the direction ofelongation of said cables.
 6. The apparatus of claim 5 wherein said oneof said frame means includes means for engaging said splice block tolimit motion of said one frame means relative to said splicing blockalong the direction of elongation of said cable.
 7. The apparatus ofclaim 6 wherein said one of said frame means engaging said splice blockfurther includes a vertical aperture communicating the upper side ofsaid jack with said splice block for receiving an inclined tool to tappermanent gripping means into corresponding seating apertures of saidsplice block.
 8. The apparatus of claim 5 wherein said sets of cablescomprise a first pair of cables having centers de-fining a verticalplane and a second pair of cables having centers defining a horizontalplane, and wherein each of said throughways of said yoke frame meanscomprises a gen-erally vertical groove for receiving the uppermost ofsaid pair of cables defining said vertical plane.
 9. Apparatus forapplying tension to first and second sets of cables extending inopposite directions in a concrete structure and secured at theirrespective remote ends to said structure and including free endsextending into a pocket in said structure in overlapping relation, thecables of each set being spaced from one another and the cables of eachset defining a plane with the planes so defined intersecting oneanother, comprising: first and second cylinder and piston rod unitsextending in a direction of elongation of said cables when placed inoperative relation relative to said cables and lying on either side ofsaid cables when in said operative position; first yoke frame meansinterconnecting the rods of said units and adapted to fit over the topsof said cables and including an element formed and adapted to receive asplice block secured to one of said sets of cables; said elementincluding a flange extending transversely to the axes of said cylinders,said flange being spaced from said first frame means to provide anabutment for the side of said splice block,and second yoke frame meansinterconnecting the cylinders of said units and adapted to receive allof said cables in a direction perpendicular to the direction ofelongation of said cables, said second frame means providing a bearingsurface for engaging a temporary fitting releasably secured to the otherof said sets of cables and remotely located from said element.
 10. Amethod of tensioning a concrete structure comprising forming said slabwith an open pocket and first and second sets of cables extending intosaid pocket out of opposing surfaces of said pocket respectively,passing said first set of cables in a first direction through a firstset of apertures in a splice block, passing said second set of cables ina direction opposite to said first direction through a second set oftapered apertures in said splice block in the direction of expandingdiameter of said apertures, securing said first set of cables to saidsplice block, passing a tapered grip on each of said second set ofcables adapted to be received in an associated one of said taperedapertures in said spice block, then forcing said second set of cablesagainst said splice block by hydraulic means to pull said second pair ofcables through said splice block thereby to tension all of said cables,then urging said tapered grips into contact with the seating surface ofsaid second set of apertures, and then releasing the force exerted bysaid hydraulic means on said cables to thereby seat said tapered gripsin their associated apertures and to connect all of said cables directlyto said splice block.
 11. A fluid pressure operated jack assembly forapplying tension to cables embedded in concrete including a pair offluid cylinders, a first yoke spanning said cylinders and fixed thereto,a second yoke fixed to the piston rods of said cylinders, said yokesbeing formed and adapted to hold said cylinders in spaced, generallyparallel relatIon, said first and second yokes having recesses formedtherein to permit passage of cables through said yokes, the recess ineach yoke providing spaced abutment surfaces extending generallyparallel to the axes of said cylinders, and a cable receiving groovebetween said abutment surfaces, said abutment surfaces being spaced fromsaid groove by additional surfaces extending between said abutmentsurfaces and said groove.
 12. The structure of claim 11 wherein one ofsaid yokes includes spaced fingers in the recess therein, the spacebetween said fingers communicating with said groove, said fingers beingspaced from said abutment surfaces to allow reception of cables betweensaid fingers and said abutment surfaces.